A semiconductor device used, for example, for a central processing unit (CPU) reaches a high temperature during its operation. To maintain the performance of such a semiconductor device, it is important to quickly release heat from the semiconductor device into external space.
For this reason, a heat radiating component such as a heat spreader or a heat pipe is often attached to a semiconductor device to effectively release heat emitted by the semiconductor device into external space. Also, research is being conducted to improve the radiation performance (or heat radiation efficiency) of heat radiating components such as heat spreaders and heat pipes. Particularly, various technologies for plating the surfaces of heat radiating components such as heat spreaders and heat pipes have been disclosed.
For example, Japanese Laid-Open Patent Publication No. 2006-28636 discloses a composite plating layer with a high thermal emittance (or heat radiation efficiency). The disclosed composite plating layer is formed using a plating solution including water, nickel sulfate, nickel chloride, boric acid, a brightener, a surfactant, and carbon nanofibers where polyacrylic acid is used as the surfactant.
Japanese Laid-Open Patent Publication No. 2005-089836 discloses a heat radiating component including a metal part and a composite plating layer formed on the metal part. The composite plating layer includes carbon nanofibers and a plating metal and is formed by electrolytic plating using an electrolytic plating solution where the carbon nanofibers are dispersed. A part of the carbon nanofibers forming the surface of the composite plating layer is exposed without being covered by the plating metal. JP2005-089836 also discloses etching the composite plating layer formed on the surface of the metal plate to remove the plating metal in the composite plating layer and thereby to increase the amount of the carbon nanofibers exposed on the composite plating layer.
Japanese Laid-Open Patent Publication No. 2006-169609 discloses a plating solution including a metal source and carbon particles such as carbon black, carbon nanotubes, ketjen black, or graphite. The average diameter of the carbon particles is less than or equal to 1 μm. When used for surface treatment of a contact member, the disclosed plating solution reduces the contact resistance of the contact member and also prevents foreign substances from adhering to the contact member. JP2006-169609 also discloses a contact member having a particle-containing-metal layer including carbon particles. According to JP2006-169609, the carbon particles are preferably exposed on the surface of the particle-containing-metal layer. Further, JP2006-169609 discloses that a metal plating layer may be formed on the surface of the particle-containing-metal layer and the carbon particles are preferably exposed on the surface of the metal plating layer.
Japanese Laid-Open Patent Publication No. 2005-320579 discloses an agglomerated particulate matter formed by carbon nanotubes. A metal plating layer is formed on at least a part of the surface of each of the carbon nanotubes. The carbon nanotubes are bonded to each other via the metal plating layers and the ends of the carbon nanotubes are not exposed and do not protrude from the agglomerated particulate matter.
Thus, various technologies for plating the surfaces of heat radiating components such as heat spreaders and heat pipes have been disclosed and many of the disclosed technologies use carbon materials such as carbon nanofibers.
To improve the heat radiation efficiency of a heat radiating component, it is necessary to increase the amount of carbon materials such as carbon nanofibers on the surface of a metal part constituting the heat radiating component.
However, with the technology disclosed in JP2006-028636, it is difficult to sufficiently improve the heat radiation efficiency. This is because even if the amount of carbon nanofibers dispersed in a plating solution is increased, some of the carbon nanofibers fall off during an ultrasonic vibration process. For example, if the carbon nanofibers on the surface of a metal part are completely removed by ultrasonic vibration, the heat radiation efficiency is reduced to one half of that before the carbon nanofibers are removed.
With the technology disclosed in JP2005-089836, the composite plating layer formed on the surface of the metal plate is etched to remove the plating metal in the composite plating layer and thereby to increase the amount of carbon nanofibers exposed on the composite plating layer. However, since a certain amount of the carbon nanofibers fall off during the etching process, it is difficult to increase the amount of carbon nanofibers exposed on the surface of the composite plating layer as desired.
With the technology disclosed in JP2006-169609, the carbon particles are exposed on the surface of the particle-containing-metal layer or on the surface of the metal plating layer formed on the particle-containing-metal layer. With this configuration, similarly to the configurations disclosed in JP2006-028636 and JP2005-089836, the carbon particles may easily fall off from the surface. Also, although the disclosed plating solution reduces the contact resistance and prevents adhesion of foreign substances, it is not clear whether the disclosed plating solution improves the heat radiation efficiency.
Further, since the carbon particles are not hydrophilic, it is difficult to reliably form the metal plating layer on the particle-containing-metal layer, so that the adhesion between the two layers tends to become low.
With the technology disclosed in JP2005-320579, it is difficult to sufficiently improve the heat radiation efficiency because the carbon nanotubes are completely covered by the metal plating layer.
Meanwhile, Japanese Laid-Open Patent Publication No. 2010-192661 discloses a technology where a composite plating layer including a metal and carbon nanotubes dispersed in the metal is formed and the composite plating layer is heated to melt the metal so that the surfaces of the carbon nanotubes are coated with the metal due to the capillary action. Here, the melting point of a metal is generally high. For example, the melting point of nickel (Ni) is about 1455° C., the melting point of iron (Fe) is about 1535 ° C., the melting point of copper (Cu) is about 1084 ° C., and the melting point of aluminum (Al) is about 660 ° C. Therefore, when, for example, nickel (Ni) is used as the metal, it is necessary to heat the composite plating layer to a temperature of about 1455 ° C. or higher. Also, this makes it necessary to use a material with a melting point higher than that of the metal for a radiator plate used as the base. Thus, the disclosed technology imposes constraints on a production process and selection of materials and is therefore difficult to implement.